A frame grabber processing board is used to enhance or otherwise modify a video image. It digitizes an input analog video signal and stores digitized data for an entire screen in a frame buffer. The stored digitized data can then be analyzed or modified to achieve desired results when converted back to an analog video signal and outputted to a cathode ray tube (CRT) display.
A color video input signal includes three analog signals (for red, green, and blue), the magnitude of the signal indicating the brightness of the red, green, or blue light making up the image. What the human eye perceives as yellow, pink, purple, etc. on a color CRT screen are actually mixtures of the primary colors: red, green, blue. Because humans do not perceive colors as relative proportions of red, green, and blue (RGB) light, processing color video signals is not straightforward using RGB data.
RGB data have been converted in the prior art using known equations implemented in software into hue (the actual color), saturation (the deepness of color; e.g., pink is desaturated red), and intensity (the light energy of a color. i.e.. brightness) data. These data describe the color that is viewed in terms that more directly relate to the viewer s perception, permitting the user to identify and modify the colors more easily. Conversions between the RGB color model and other color models are described in Foley, J. D. Fundamentals of Interactive Computer Graphics, (Addison-Wesley 1982) pp. 602-622; Ohta, Y. et al., "Color Information for Region Segmentation", Computer Graphics and Image processing. Vol 13, (1980), pp. 222-241; and Smith, A. R., "Color Gamut Transform Pairs" Proc. of Annu. Conf. on Comput. Graph. and Interact Tech., Aug. 23-25, 1978, published by SIGGRAPH-ACM NY, NY, pp. 12-19.
Dalke et al. U.S. Pat. No. 4,183,046 recites transforming source data representing an actual image using software, firmware, or hardware into digital hue, saturation and intensity (HSI) data stored in a memory. The stored saturation and hue data are used to address red, green, and blue look-up tables (programmable read only memories) to obtain red digital data, green digital data, and blue digital data that are in proper proportion to provide the desired color when converted to RGB analog signals and displayed on a CRT. The stored intensity data are used to control the magnitudes of the RGB analog signals.